1. Field of the Invention
The present invention relates to a bus driver integrated circuit for driving a bus, and particularly to a bus driver integrated circuit having a reduced integrated circuit area.
2. Description of the Prior Art
Generally, a bus driver which is used for bus driving in a microprocessor has sufficient driving ability for driving heavily loaded wiring. FIG. 1 is a compositional diagram of a bus driver 100 which is conventionally used. The bus driver 100 is so arranged that an enable signal E and a data signal A are inputted to input terminals of a NAND gate 101 and a NOR gate 102 respectively. Further, the enable signal E is also inputted to the NOR gate 102 through an inverter 103. An output terminal of the NAND gate 101 is connected to a gate electrode of a P channel MOS transistor (PMOS transistor) P.sub.1. The output terminal of the NOR gate 102 is connected to a gate electrode of an N channel MOS transistor (NMOS transistor) N.sub.1, and an output Z is obtained from a connection point of transistors P.sub.1 and N.sub.1. Reference character V.sub.DD designates a power source.
Accordingly, an output of the NAND gate 101 becomes 0 only when A is 1 and E is 1, and P.sub.1 becomes ON. While, an output of the NOR gate 102 becomes 1 only when A is 0 and E is 1, and N.sub.1 becomes ON. Thus, the bus driving is performed.
FIG. 2 is a compositional diagram of a bus driver system 200 in which is employed the bus driver 100. In the same diagram, the bus driver system 200 is used for an internal bus having relatively small wiring load. In the diagram, reference numerals 201, 202, 203, 204, 205, . . . , IN are respectively composed of the bus drivers 100, and these drive main buses 0, 1, . . . , n respectively.
More specifically, these bus drivers are respectively composed of the NAND gates 101, NOR gates 102 and inverters 103.
However, in the internal bus system having relatively small wiring load as shown in the same diagram, since the bus drivers 201, 202, 203, 204, 205, . . . , I.sub.n respectively use bus drivers which are used for a bus system having large wiring load, it is difficult to reduce an area of a bus driver integrated circuit which employs such a bus driver system. Accordingly, an entire and actual pattern area of the integrated circuit becomes inevitably large.